1. Field of the Invention
This invention relates to a semiconductor laser which achieves expansion of the oscillation spectrum width, resulting in the reduction of coherency of the oscillation spectrum.
2. Description of the Prior Art
Semiconductor lasers have been used as light sources such as for the regeneration of optical discs, for optical-measuring systems, and for optical communication systems. However, noise is produced with these semiconductor lasers due to reflected light from the optical systems, which makes it difficult to establish precise optical systems incorporating the semiconductor lasers.
The inventors of the present invention have developed a semiconductor laser which comprises a striped structure achieving self-excited oscillation due to relaxation fluctuation of carriers in semiconductor materials to thereby attain oscillation with a great spectrum width, resulting in a semiconductor laser in which noise due to reflected light can be suppressed (Appl. Phys. Letter., vol. 43, No. 3, 1983, pp 219). However, in this semiconductor laser, the oscillation wavelength is modulated by a specific frequency, resulting in an oscillation spectrum with dual peaks, as shown in FIG. 3(a), each of which is steep. Therefore, this semiconductor laser cannot attain the reduction of coherency of the oscillation spectrum.